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August 13

Who burns more calories

I was reading calories burnt per hour lists of various sports and it got me thinking, would a fat out of shape person spend more calories than a fit person in the same activity even if he did less of it? For example if a fat guy runs for 10 minutes and is absolutely exhausted and faints would he spend more energy than a fit person who runs 20 minutes and does not even feel tired? — Preceding unsigned comment added by 88.195.215.49 (talk) 07:34, 13 August 2013 (UTC)

(Note: Wikipedia does not offer medical advice - this is not authoritative) There is a distinction to make between the amount of fat burned and energy spent. The answer is that it depends, based on how efficient that fat person is, the weights of both, the exercises involved, the conditions, and the exact lengths of time.--Jasper Deng (talk) 07:45, 13 August 2013 (UTC)

Your question can't be answered as asked, but a few things to help you on your way:

How exhausted a person feels is not a measure of how much energy they've used. If two persons ride exercise bikes and spend the same amount of calories in the same time the person in better shape will feel less exhausted even if they spent the same number of calories.

Generally speaking, a heavy person will burn more calories per mile running, but it depends very much on how efficient that person's running style is, and to some extent on the speed. Sjö (talk) 08:22, 13 August 2013 (UTC)

I'm aware of formal measurements that are made on people with physical disabilities, such as cerebral palsy, that demonstrate that such people use considerably more energy than able bodied people to perform the same task. It's reasonable to guess that obese people would too. HiLo48 (talk) 08:14, 13 August 2013 (UTC)

See here for some figures. Count Iblis (talk) 12:49, 13 August 2013 (UTC)

• Muscles have a much higher resting metabolism than fatty tissue, burn more calories, and require a specific diet to maintain at a weightlifting level. See Basal metabolic rate. μηδείς (talk) 23:30, 13 August 2013 (UTC)

I remember an experiment we did at school which is different but related. Everyone had to run up a few flights of stairs and was timed doing it. We calculated how much energy you burned (weight times height) and divided it by the time, the theory being that the more energy you can produce in the shorter amount of time is basically how "fit" you are. Turns out, the most overweight people, even thought they were slower, were actually the most "fit" and the most skinny people were the least fit. Of course this is purely by people's energy output, it says absolutely nothing about health. Vespine (talk) 02:20, 14 August 2013 (UTC)

That power must be divided by the weight to obtain the power/weight ratio, which is a good emasure for fitness (You need to be above 3 Watt/kg), so the speed itself is actually a good measure for fitness although one should look at exertions that last for more than 12 minutes (so, you could look at how fast people are able to climb the Empire State Building). Count Iblis (talk) 17:51, 14 August 2013 (UTC)

Seat collision for swing ride caused by wind - how?

WindSeeker is closed during high winds, evidently because its seats, probably even despite the dampers present, collide when the air is in motion. The article, not unexpectedly, doesn't discuss the physics.

So, I did a thought experiment for a very simple case, where the velocity field of the wind is constant, and the air density is assumed constant. I know these are approximations that are probably not valid in real life, but I first figured I should start with this special case, where the simple drag equation is at least approximately applicable. I then made the assumption that the hinges attaching each seat's support bar to the rotating gondola allowed complete freedom of motion (again, the dampers are there to hinder it, but again, I have to simplify the problem a bit), thus not considering the friction of the hinge. With this, I began doing the vector addition of the wind's and seat's velocity fields so I could then calculate the drag force with the resultant relative air velocity. However, doing it mentally, it still didn't quite dawn on me why this should cause the seats to collide, nor the maximum safe wind velocity predicted by my simple model. I don't have a very advanced understanding of fluid dynamics, so I wish the relatively simple drag equation will suffice to model this situation.

While I'm willing to accept a vector calculus explanation (and half-expect one), I'm sure the physics can't be that hard (although with a non-constant force field, I've already fixed my mind on the need to perform integration here).--Jasper Deng (talk) 08:09, 13 August 2013 (UTC)

I think it's simply that your assumption of a constant wind isn't valid. Air, like water, contains currents, where winds are higher or lower, and in different directions, and modeling this is necessary to understand the problem. StuRat (talk) 09:31, 13 August 2013 (UTC)

Even starting with a 'constant velocity wind', you can end up with oscillations - see vortex shedding. AndyTheGrump (talk) 22:11, 13 August 2013 (UTC)

Theory of Relativity

We know that maximum speed of a body can be as high as the speed of light. Now my question is that - Imagine a train is running with the speed a light and a boy runs in the train. An observer outside the train sees that boy. Then what is the speed of the boy with respect to the observer outside? If you are thinking to add the speed of the train and the boy, then it would be more than the speed of the light that is impossible.Publisher54321 (talk) 09:49, 13 August 2013 (UTC)

For the boy to run in the train, he would have to accelerate himself. But since he already has infinite mass, he can't. The situation cannot arise. 1.122.88.140 (talk) 09:59, 13 August 2013 (UTC)

And just to be clear, the reason that he cannot accelerate while he has an infinite mass, is because to accelerate any infinite mass, you need an ifinite amount of energy, which is not available in this universe. --Lgriot (talk) 11:09, 13 August 2013 (UTC)

The above are remarkably misleading answers for what is the most fundamental thought experiment that underpins all of special relativity. The notion that that boy cannot accelerate coz he is nearing infinite mass only begs the question as to why that is so? The simple answer is that at close to light speeds, velocity is not cumulative as in a normal train. We always see light moving at the same speed regardless of whether it is coming from an object moving towards us or away from us. Because we never see something move faster than speed of light, then, in the boy in train case, we see time in the train slow down, and the boy seems to be running in slow motion as the train approaches the speed of light. If the train could achieve light speed, then the boy would be like a photo or statue of himself, totally unmoving, and both he and the train would be moving at the same speed - light speed. To the boy, tho, nothing has changed inside the train, and he moves as per usual. The time dilation and mass increase business are consequences of the unchanging nature of the speed of light. Of course, all this has been confirmed in many experiments since Einstein. Calculations to get the geo-positioning satellites to orbit correctly must include factors that take account for the fact that their time slows down as they pick up speed. Myles325a (talk) 02:18, 18 August 2013 (UTC)

Those answers are a bit misleading. In the reference frame of the train, the boy can accelerate in a perfectly normal way. But in the reference frame of an observer who sees the train moving at nearly the speed of light, time dilation causes the boy's acceleration to appear very small. Looie496 (talk) 14:52, 13 August 2013 (UTC)

No I beleive that your answer is misleading, Looie, becuase you didn't properly read the (poorly worded, fair enough) question. The OP did not ask about a train going near the spead of light, but at the speed of light. --Lgriot (talk) 08:21, 14 August 2013 (UTC)

The relativistic answer (for speeds below c) is given by Velocity-addition_formula#Special_theory_of_relativity. AndrewWTaylor (talk) 11:54, 13 August 2013 (UTC)

It also work for speeds at c. Dauto (talk) 14:40, 13 August 2013 (UTC)

Has anyone noticed that this is a slight modification of the very thought experiment used by Einstein when he created the theory of relativity? Plasmic Physics (talk) 11:59, 13 August 2013 (UTC)

I wouldn't draw any inferences. — Quondum 12:09, 13 August 2013 (UTC)

Strangely, I don't recall the flashlight-on-the-train explanation actually being concocted by Einstein, even though "everybody" knows that Einstein used a flashlight on a train as his example for special relativity. That example doesn't appear in the famous 1905 papers, (available in English translation on Wikimedia and at Mr. Walker's excellent website).

So, how did this bit of historical corruption occur? Who concocted a flashlight-on-a-train gedankenexperiment, and why does everybody attribute it to Einstein!? It would seem that science, like religion, is easily corrupted over the course of history, by people's relentless insistence to deify individual contributors and give them credit for creation of everything.

Einstein wrote many things, and originated many ideas. Einstein wrote about electromagnetic wave dynamics, and corpuscles of light, and some very convoluted mathematics about geometric identities between geodesics and inverse-square-law forces; (and plenty more about incorrect theoretical arcana about spectral lines that nobody ever mentions any more because it was totally wrong).

But so did thousands of other physicists. Those more-anonymous physicists had lesser egos, worse publicists, and more comprehensible writing. I put forward the bold statement: nearly everything that we know today about the photoelectric effect, the mechanisms of special and general relativity, electrodynamics, didn't come from Einstein.

So, a challenge to the reference desk: which scientist or author first published a parable of a flashlight on a train (or a person running on a train) moving with relativistic velocity? Nimur (talk) 12:45, 13 August 2013 (UTC)

Oh, Nimur. You can be such a grouch. Dauto (talk) 14:40, 13 August 2013 (UTC)

Sorry, I'll try to be more cheerful! Happy Tuesday, here's a bit of fun science-fiction to brighten your morning... actually it's probably the reason I'm so grouchy today. Let's all just conveniently forget to account for the energy consumption of the thousands of jet-engines you need to evacuate a 700-mile metal tube, and pretend that you can put an airtight metal tube in California's central valley and model its air-temperature at 68° F! Also multiply the air-compressor's required horsepower by ten in every sixth paragraph and neglect to update your overall energy budget! And vomit-inducing 3-mile-radius turns at 760 miles per hour! At least the cartoons are pretty. Nimur (talk) 15:39, 13 August 2013 (UTC)

Thanks! I was looking for the tech details earlier but missed them. Curious to observe the walls are 0.8-0.9 inch thick. [1] Wnt (talk) 22:54, 13 August 2013 (UTC)

So you admit it, not even you know who said it first? Well, I hate to pop your bubble, but I never said Einstein was the first either. So, I may yet be vindicated. Plasmic Physics (talk) 19:13, 13 August 2013 (UTC)

I admitted nothing except being slightly grouchy! Nimur (talk) 20:41, 13 August 2013 (UTC)

So, I will not be vindicated, nevertheless, my preceding statement still remains true. Plasmic Physics (talk) 21:39, 13 August 2013 (UTC)

I don't know if the question has been answered yet. I would add that just because something is not theoretically impossible, does not mean it is possible in practice. I suspect that even though relativity says mass can't travel FASTER then the speed of light, I bet that in practice mass (more then a handful of particles anyway) can't travel AT or even very near to the speed of light either. Vespine (talk) 02:05, 14 August 2013 (UTC)

"Near the speed of light" is easy: just use a reference system in which the thing has a sufficiently high speed.--Wrongfilter (talk) 12:13, 14 August 2013 (UTC)

I actually don't think I really get that yet, it hurts my brain. Vespine (talk) 22:56, 15 August 2013 (UTC)

However, I think my point is that nothing actually occurs in those "reference systems" apart from maybe cosmic rays. Things that are more then a molecule or a few, relative to eachother in the whole universe only differ by a few percent of the speed of light, as far as I can gather from some quick googling Vespine (talk) 23:37, 15 August 2013 (UTC)

Vespine said 'I suspect that even though relativity says mass can't travel FASTER then the speed of light, I bet that in practice mass (more then a handful of particles anyway) can't travel AT or even very near to the speed of light either. ' Actually light itself (photons) have mass (no rest mass) but do travel at and near the speed of light. Technically, since space actually has matter in it, and matter slows down light, even light cannot travel at 'c', but that is no longer in the theoretical realm. Jokem (talk) 23:50, 18 August 2013 (UTC)

Asthma

If a non-asthmatic person uses a Metered-dose inhaler, will it aid them in completing a marathon? Pass a Method talk 12:49, 13 August 2013 (UTC)

If it would give an appreciable advantage it would be banned from use in the sport. So, if it hasn't been banned then it has no effect. I guess it'd be treating a condition the runner doesn't have so would not improve the running. (But it could make it much worse and be unsafe.) The inhaler is for reducing constriction of the airways; do marathon runners have constricted airways as a limit on their running? RJFJR (talk) 16:14, 13 August 2013 (UTC)

Obviously that depends on what's in it. There are quite a variety of drugs that can be absorbed into the lining of the lungs - and any one of them might be dispensed this way. The more common anti-asthma drugs are corticosteroids - and steroids are pretty much banned in events like marathons - so I'm guessing they would be illegal. Whether they'd help or not is different matter. I doubt it...but I could easily be wrong. SteveBaker (talk) 16:23, 13 August 2013 (UTC)

Inhaled steroids are corticosteroids, not anabolic steroids, and I'm not sure the former would be performance-enhancing. Inhaled beta agonists might or might not help depending on the athlete and conditions. -- Scray (talk) 21:35, 13 August 2013 (UTC)

T%he standard emergency inhaler is Salbutamol - our article covers its ban in sports and the contradictory studies of its effect on healthy subjects. Rmhermen (talk) 13:07, 14 August 2013 (UTC)

Everyone has constriction of the airways to some degree. When it gets to the point where it becomes an illness, then an inhaler or some other medical aid is necessary. How much it opens up the airways and how much it aids in the exchange of blood gasses would tell you how much of an advantage it gives. Jokem (talk) 00:13, 19 August 2013 (UTC)

Origins Of The Universe: Steady State & Big Bang Theories

What are some of the current problems and limitations of the steady state and big bang theory? 220.233.20.37 (talk) 12:57, 13 August 2013 (UTC)

For the Big Bang theory, you shoud read the article Inflation (cosmology). The steady state theory has long been debunked, you can read our Wiki articles on that subject. Perhaps also articles on Fred Hoyle (had it not been for Hoyle, steady state would have died decades earlier). Count Iblis (talk) 13:07, 13 August 2013 (UTC)

Right now, steady-state is busted, dead, gone, impossible - it's up there with "Adam and Eve" and "the Great Arklesiezure". Not even worth discussing. The Big Bang is really the only theory that explains everything - and the discovery of the cosmic microwave background radiation more or less sealed the deal. The problems are really details that are unrelated to the core fact - What caused it? What was before it? How will the universe end? What the heck is it with all of this "Dark" stuff? Those would be problems with whatever theory you might come up with though, it's not entirely clear whether the fact of the big bang has any impact on those questions. SteveBaker (talk) 16:20, 13 August 2013 (UTC)

Adam and Eve still works as a sociological metaphor, so the Steady-State theory is even less credible than Adam and Eve. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:31, 13 August 2013 (UTC)

There are still some die-hards out there such as Jayant Narlikar who maintain that the steady-state theory is viable. In his book The Primeval Universe he postulates that the microwave background radiation is due to blackbody radiation associated with helium production in stars (of necessity, the steady-state theory requires something to be making all the helium that is otherwise accounted for by the big bang). Mr. Baker, please don't shout at me, I didn't say I supported this theory. SpinningSpark 00:46, 14 August 2013 (UTC)

In relativity, whether actual mass changes or not

According to Einstein's theory of relativity, mass of a body increases when its speed or motion increases. Therefore, there is a considerable increase in mass of a body moving with a speed of 100000 km/sec. On the other hand, we know, motion of any body in Universe is relative. The body moving with the speed of 100000 km/sec must be at rest with respect to some other object in Universe, hence according to this situation there should be no change in mass. I am confused because in the first case its mass seems to change, but in the second case its mass seems to be constant. Again, this body is in motion as well as in rest with respect to two different reference frames. What should I conclude from this? Whether the mass of the object changes or remains constant? I think the correct explanation for this would be the change in mass due to speed or motion of an object depends on the relative motion of that object with respect to the reference frame from which the motion of that object is being observed. Hence, the mass of that object would be different for different frames having different relative speed with respect to that object. Correct me if I am wrong. Thanks for bearing me! Publisher54321 (talk) 18:08, 13 August 2013 (UTC)

Someone will be along shortly to explain the details, but I'm pretty sure the answer to your question can be gained from a careful reading of relativistic mass and rest mass. SemanticMantis (talk) 18:12, 13 August 2013 (UTC)

Changing to a different reference frame changes the object's velocity thus its kinetic energy (and mass per mass-energy equivalence) does indeed differ, but remember that the coordinate change applied to the object also must be applied to all other objects, thus it doesn't matter whether the ball has the energy that hit the ground or the ground it... (I wonder if it will be friends with me...) the dynamics are the same. You said the object gained mass accelerating, but incorrectly stated this: "The body moving with the speed of 100000 km/sec must be at rest with respect to some other object in Universe, hence according to this situation there should be no change in mass." However, it would have been decelerating in the new reference frame thus losing speed and mass-energy in the process until it was at rest. -Modocc (talk) 18:53, 13 August 2013 (UTC)

(edit conflict)(In the absence of an expert ... ) The rest mass (as measured in an inertial frame at rest relative to the body) remains the same in all reference frames. The preferred view is to ignore the apparent "increase in mass" because looking at the situation this way does not always give the right answer, and instead to consider the 4-D momentum vector ( but it's too long since I studied this for me to attempt an explanation!) Einstein wrote: "It is not good to introduce the concept of the mass $M=m/{\sqrt {1-v^{2}/c^{2}}}$ of a moving body for which no clear definition can be given. It is better to introduce no other mass concept than the ’rest mass’ m." Dbfirs 20:39, 13 August 2013 (UTC)

Relativistic mass is used to calculate total mass-energy (or total energy) and, for that purpose, it seems to give correct answers. Modocc (talk) 21:23, 13 August 2013 (UTC)

If you heat a body up the atoms will move faster and so the body will be heavier. Yes there is more mass. Dmcq (talk) 21:18, 13 August 2013 (UTC)

That increase of mass is due to energy in internal degrees of freedom of a composite body. Its mass (rest mass if you insist) will not change if you move the body as a whole. Similarly, the mass excess of a nucleus (possibly the clearest manifestation of E=mc²) is due to the fact that the nucleus has internal degrees of freedom. --Wrongfilter (talk) 21:30, 13 August 2013 (UTC)

Hawking radiation and the formation of black holes.

For the first part of my question, assume an observer falling in to an existing black hole which is emitting Hawking radiation. As the observer approaches the horizon, my understanding is that the observed temperature of radiation would increase, tending towards infinity at the horizon (or at least the Planck temperature shortly before the horizon). As a result, the infalling observer would observe a greater emitted power from the hole as they fell toward the horizon, and as a consequence a greater mass loss rate than an observer at infinity. So would the infalling observer see the black hole radiate itself away before they actually crossed the horizon? If so, would they see it radiate itself away before the radiation reached trans-Planckian temperatures (or, at least, would the observation of trans-Planckian temperatures be delayed until the observed remaining mass was on the order of the Planck mass)?

For the second part of my question, section 3.8 (on page 26) of this article states that a collapsing object that does not collapse to within its Schwarzschild radius will emit Hawking radiation until the collapse stops (actually it doesn't quite state that directly, it states that the object will stop emitting Hawking radiation when the collapse stops, the article is agnostic as to whether Hawking radiation is emitted from any object in the first place, but the implication seems to be that if Hawking radiation is ever emitted, it will be emitted by collapsing objects as long as the collapse continues).

So the question then is whether, as the radius of a collapsing object approaches its Schwarzschild radius, Hawking radiation in the vicinity of the event-horizon-to-be will be intense enough that the object will lose mass quickly enough that its radius is never smaller than its Schwarzschild radius? In other words, if Hawking radiation in fact occurs, does it prevent the interior portion of the Schwarzschild geometry from ever actually forming, so that objects that are asymptotically close to being black holes in terms of exterior spacetime geometry might exist, but no black holes per-se actually do exist? — Preceding unsigned comment added by Linguofreak (talk • contribs) 21:58, 13 August 2013 (UTC)

I don't understand it, but it is tied in with the Unruh effect somehow. The event horizon is a line that is continually accelerating against the rest frame. The Unruh radiation is seen because it is accelerating. If you're falling in, you're not accelerating, so what looks like an infinite energy vacuum to the event horizon looks like a just plain vacuum to you. I think. Note that there is also some absurd time dilation going on in the event horizon time frame - all that extra Hawking radiation isn't piling up in the region between event horizon and infinity, so the amount going on at any given moment (faraway rest frame time) at the event horizon must actually be very small. Wnt (talk) 23:08, 13 August 2013 (UTC)

From the point of view of the observer falling in the hole there is no Hawking radiation. Dauto (talk) 17:22, 14 August 2013 (UTC)

The answers above are correct but I want to add that the high temperature near the horizon doesn't translate to a higher rate of heat loss. The Hawking temperature is the temperature of the radiation at infinity. If you're closer than infinity (and stationary) you will measure a higher temperature, but the emitted power doesn't increase just because you made the measurement. This is the same as any other situation where there's a temperature gradient.

I'm not sure whether non-black-holes lose mass to Hawking radiation. I can't remember ever reading a text that discussed it. On the one hand, the distant gravitational field is the same and it's hard to see how the nature of the object at the center could matter that much. On the other hand, Hawking and Unruh radiation "come from" an event horizon, and there's no event horizon in this case. -- BenRG (talk) 05:31, 16 August 2013 (UTC)

AM radio reception (unconventional)

The AM radio station WLW once broadcast at 500kW, and could be heard across much of the globe. Our article says there are reports from people living near the tower, who claimed to hear broadcasts through the coils of their mattress springs:WLW#History. The cited ref acknowledges that these reports are to be treated skeptically. But I wonder: is it conceptually possible for a very high power AM broadcast at 700kHz to stimulate audible vibration in a spring? More far-fetched: is it possible for for a spring to act as antenna and speaker, so that the actual signal being sent is demodulated and heard faithfully? I've seen lots of "yes" (and "no") answers via googling, but few that were explained scientifically or inspired much confidence in their reliability/authority. Thanks, SemanticMantis (talk) 22:05, 13 August 2013 (UTC)

Seems to me there have been stories of people picking up radio frequencies in the fillings of their teeth, so anything's possible, especially if you're close to the source. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:28, 13 August 2013 (UTC)

The scientific explanation you are looking for is magnetostriction. Close to a powerful transmitter almost any piece of ungrounded metal will mechanically vibrate in sympathy with the RF transmission. I recall a case during refurbishment of the BBC's medium wave Brookmans Park transmitting station (in the 1980s iirc) that Radio 2 came blaring out of the newly replaced heating radiators because the pipework had not been properly RF earthed. All test equipment brought onto the site had to be specially custom modified for RF decoupling otherwise it would pick up the transmission rather than measure what it was supposed to be measuring. It could even be destroyed. The perimeter fence around powerful transmitting stations have to be earthed with ground spikes at regular intervals to prevent dangerous voltages being induced. SpinningSpark 00:07, 14 August 2013 (UTC)

...and I see that they are still causing problems for the local residents 30 years later. SpinningSpark 00:20, 14 August 2013 (UTC)

Lucille Ball always claimed that she could hear radio stations through the fillings in her teeth (There is a brief mention of the story in Lucille_Ball#Later_career - and a more complete rundown over on Snopes). I suspect she added much to the claim that this happens - but her story doesn't exactly hold water. She claimed to have heard a Japanese spy network transmitting somewhere in California and that her report led to them being captured. Sadly, there doesn't seem to any actual information that it really happened - so it's very likely to be a complete fabrication. But I think that her public retelling of this story in numerous books and interviews is where the whole thing started. SteveBaker (talk) 02:10, 14 August 2013 (UTC)

I challenge the claim that WLW could ever have been "heard across much of the globe." Maybe it could have been heard across much of the continental US, not including Alaska and Hawaii, but including parts of Mexico and Canada, if local stations with the same frequency engaged in a "Silent Night" wherein they shut down for an hour or so to allow local listeners to DX, as was sometimes done in the 1920's. The WLW AM frequency is probably too low for the short wave skip propagation which allows reception half the world away. And 50 kilowatts is more likely as a US "clear channel" station than the claimed 500 kW, though I stand ready to be corrected by reliable sources. Some Mexican stations might have transmitted at 500 kW. Edison (talk) 06:03, 14 August 2013 (UTC)

You may be to a certain extent wrong. The wikipedia article states that the 500 KW transmitter was used to broadcast to US troops in Europe at the close of World War 2. With tube radios featuring low intermodulation distortion, and the generally less noisy conditions before the proliferation of home elctric goods in the 1950's, 50 kW AM stations could be heard up to 2000 km away. Using 10 times the power with top loaded antennas that suppress high angle radiation, you get a bit better than root-10 times the range, ie about 7000 km in this case. While sky wave propagation requires frequencies above the AM band, the lower frequency you go, the better the ground wave follows the curvature of the Earth. Once the ground wave gets to an ocean, it follows the curvature of Earth with somewhat less attenuation. So coverage of at least half the surface of the Earth is possible, perhaps more. 1.122.88.140 (talk) 06:54, 14 August 2013 (UTC)

• Thanks all, especially SpinningSpark. So, it seems that getting audible vibration is fairly reasonable with the right setup. I understand why e.g. fences would need grounding to shunt off induced currents, and the basic idea behind magnetostriction. But I'm still confused on how a single spring or radiator (no resistors, transistors, etc) could act to demodulate an AM signal, so that the actual broadcast is heard, and not just some rhythmic "vibration in sympathy". Wouldn't it have to do something similar to that described at Demodulate#AM_radio? I suspect that this would rely on some really good luck regarding the nature of the spring, and the frequency of broadcast. That is, I don't expect to have any old spring act as a complete radio whenever it's sufficiently close to a powerful broadcast. Does that sound right? Bonus question: could I "tune" a spring to work this way for a specific broadcast tower/frequency, provided that I can get rather close to a 50kW AM tower? SemanticMantis (talk) 15:37, 14 August 2013 (UTC)

  Magnetostriction is inherently non-linear. In mechanical filters that use magnetostrictive transducers, small magnets are sometimes placed near the transducers to bias them into a near linear region, much as DC bias is used to bring a transistor into a linear region. If you are looking to make the mechanical equivalent of a diode in your spring experiment you could attach a rod to one loop of the spring and then place a stop to catch the rod in one direction. This effectively acts as a mechanical diode. SpinningSpark 19:41, 14 August 2013 (UTC)

Thanks again! SemanticMantis (talk) 20:40, 14 August 2013 (UTC)

Resolved

August 14

Ship traffic controller

Is there some kind of ship or sea traffic controller for straights and such? Or how do they know that ships won't crash? OsmanRF34 (talk) 00:56, 14 August 2013 (UTC)

If by controllers you mean the equivalent of air traffic controllers then no, they do not exist in international waters. However, in some busy lanes there are Traffic Separation Schemes where conventions are set by the International Maritime Organization that all ships are expected to follow. An example is the Dover Traffic Separation System which covers the busiest shipping route in the world, the English Channel. SpinningSpark 01:20, 14 August 2013 (UTC)

Air traffic controllers operate mostly only around airports right? Not general "international air space". Similarly, I thought shipping ports had controllers. There is a big tower at the port near where I work that even looks like an air traffic control tower. The only reference I could find after a very quick search is this [about the control at Sydney harbor. Vespine (talk) 01:28, 14 August 2013 (UTC)

Ports tend not to be in international waters. That is a very different situation. Shipping will be controlled by the port authority and ships will often be required to take a local pilot on board while entering and exiting. Your statement about air traffic controller is also incorrect. Regions outside airports can also be controlled airspace - airways for instance. In England there is almost nowhere that is not controlled airspace by someone. See also North Atlantic Tracks as an example of controlled airspace in international airspace over the Atlantic. SpinningSpark 01:52, 14 August 2013 (UTC)

The most accurate way to say it then would then be, in some places yes, but in most places no. Mingmingla (talk) 03:59, 14 August 2013 (UTC)

Not all air traffic controllers work at an airport, see Area Control Center. Some of those controllers may be responsible for international air space. CambridgeBayWeather (talk) 05:54, 14 August 2013 (UTC)

Straits as well as ports may require pilots. See [2] to hire a pilot for the Detroit River (err, strait) Rmhermen (talk) 12:51, 14 August 2013 (UTC)

• Harbor master μηδείς (talk) 23:56, 14 August 2013 (UTC)

There's something like this for monitoring shipping in the international Strait of Juan de Fuca and other nearby waterways—major shipping routes to nearby ports in Seattle, Vancouver, and others. Overview here. Vessel traffic centers monitor the larger ships, which are required to report by voice. Traffic control apparently gives direct navigational orders about 30 times a year to prevent collisions. It's basically a Traffic Separation Scheme, but with "extra stuff" for dealing with ships leaving the Strait of Juan de Fuca via a number of other straits, some in Canada and some in the US. The charts for the eastern end of the Strait of Juan de Fuca are rather complex. Pfly (talk) 03:10, 17 August 2013 (UTC)

How is this slide possible?

Can anyone enlight me how come the car in this [3] doesn't flip over? It's sliding some fair distance, velocity perpendicular to the wheels direction. How is that possible? Zarnivop (talk) 13:11, 14 August 2013 (UTC)

C'mon, it's 9GAG, it's probably manipulated or something. ☯ Bonkers The Clown \(^_^)/ Nonsensical Babble ☯ 13:14, 14 August 2013 (UTC)

Loose dirt. Low center of gravity. Professional driver. --Onorem (talk) 13:19, 14 August 2013 (UTC)

Drifting (motorsport) - In the interest of actually also providing a ref. --Onorem (talk) 13:24, 14 August 2013 (UTC)

The video looks speeded up to me. Otherwise, it looks like fairly typical rally driving on a low-grip surface. AndyTheGrump (talk) 13:20, 14 August 2013 (UTC)

See also Scandinavian flick. AndyTheGrump (talk) 13:28, 14 August 2013 (UTC)

Excellent, Top-Gear DID flip-over. So it's a pro-biz: modified car, pro driver, weight shifting galore. Thank you. Zarnivop (talk) 16:51, 14 August 2013 (UTC)

If you read it carefully, Top Gear (note the lack of hyphen) flipped over a van while trying to do a flick. Slight difference between a commercial van and a rally car..... Also, no pro driver required, again if you read the Scandinavian Flick article you'll see this is regularly taught in driving classes in Scandinavia 82.0.112.151 (talk) 22:02, 14 August 2013 (UTC)

Stunt driver, possibly attempted many times until they got it just right. Kind of like that one scene in The Blues Brothers where they go into a 180 spin and come to a stop perfectly in a parallel-parking spot next to a restaurant. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:11, 15 August 2013 (UTC)

I wonder if the wheels and other turning parts inside cause a gyroscopic effect that contribute resistance to flipping. Richard-of-Earth (talk) 08:28, 15 August 2013 (UTC)

The gyroscopic effect is not very important for racing cars, but plays a major role for racing motorcycles. Dauto (talk) 15:09, 15 August 2013 (UTC)

Fatty acids and the brain

Why does it say in Fatty acid, "Despite long-standing assertions to the contrary, the brain can use fatty acids as a source of fuel", but in starvation response, it says, "Fatty acids can be used directly as an energy source by most tissues in the body, except the brain, since they are unable to cross the blood–brain barrier." ScienceApe (talk) 16:43, 14 August 2013 (UTC)

It looks like you've uncovered an inconsistency, and a way to make WP better. Thanks! The first sentence has two cited sources, here [4], and here [5]. The first one specifically says "Glucose is the dominant oxidative fuel for brain, but studies have indicated that fatty acids are used by brain as well." The second one is titled, in part "Heptanoate as a neural fuel:" These are from reputable journals, 2003, 2012, respectively, and they both seem to say that the brain can use fatty acids, despite what we used to think. So I'd say that the starvation response article should be modified to say simply "Fatty acids can be used directly as an energy source by most tissues in the body." But I'm not feeling very bold at the moment, and this is far from my expertise. SemanticMantis (talk) 20:36, 14 August 2013 (UTC)

After thinking a bit and reading more of the sources, I felt bolder and removed the claim that fatty acids cannot be used by the brain from starvation response. If someone thinks I got it wrong, they can revert. SemanticMantis (talk) 22:56, 14 August 2013 (UTC)

Emergency medical technician training I received indicated that due to the brain's inability to process any blood-borne energy source except glucose, low glucose levels in the blood will be fatal unless corrected promptly. However, this information was given in a lecture and I don't have a published source for it.

It is conceivable that the brain might be able to make some use of energy sources other than glucose, but not at at a high enough level to sustain life in the absence of glucose. You might reexamine your references with that possibility in mind. Jc3s5h (talk) 23:15, 14 August 2013 (UTC)

Well, the story I'm seeing is basically that a long-held belief has been overturned by more recent evidence. That scientists and textbooks used to say: "fatty acids cannot cross the blood-brain barrier, and cannot be metabolized by brain tissue". More recently, research has shown that at least some fatty acids can be metabolized in some circumstances. That doesn't at all contradict what you report from EMT training. Indeed, the sources above make it seem like fatty acids contribute a very small part to the overall brain metabolism budget. My point is, if there is even one exception to this "rule", then there's no need for an article to go out of its way to mention it. What is probably called for is that the starvation response article have a short paragraph about how extended low blood glucose is bad for the brain, because glucose is the primary source of energy, etc. But I can't write that. What I can do is delete an unnecessary reference to a likely outdated/wrong "rule". Again, I'm no expert, and I have no horse in this race. It is a great question here though, because it will (hopefully) get more expert users and references to help clarify the issue :) SemanticMantis (talk) 23:42, 14 August 2013 (UTC)

The brain also can metabolize alcohol: "Some alcohol metabolism also occurs in other tissues, including the pancreas (3) and the brain, causing damage to cells and tissues (1)." from National Institutes of Health (USA). Edison (talk) 01:23, 15 August 2013 (UTC)

August 15

Binary star systems and their planets

In sci-fi shows, planets with multiple suns are often shown. Are the distances between binary systems really small enough to allow a planet to be significantly affected by both stars, to the point where they can be seriously seen to have "two suns" by an observer on the surface? 2.223.230.86 (talk) 01:32, 15 August 2013 (UTC)

For some binary systems, yes. See Alpha_Centauri_B#Theoretical_planets for some discussion, as well as an artist's rendition of what such a sky would look like. However, in this case the planet would be in the ballpark of 10 times closer to one star than the other to be in a habitable zone, so you would never see two huge suns in the sky. Someguy1221 (talk) 01:39, 15 August 2013 (UTC)

The OP didn't specify that it has to be a habitable planet. Also, sometimes one star is more than 10X the diameter of another. I wonder if a planet can exist at the barycenter between the two stars, or at Lagrange points between them. StuRat (talk) 07:43, 15 August 2013 (UTC)

Planets have been discovered orbiting close binary stars at a larger distance, like at Kepler-47.

A planet placed (with 0 velocity) at the barycenter the planet would start falling towards the heavier star, and wouldn't have a stable orbit; and the Lagrange point L1 isn't the place for a stable orbit either. There are stable orbit around the Lagrange points L4 and L5 if one star is a lot more massive than the other (like the Trojan asteroids of Jupiter), and also around both of them (horseshoe orbit). Icek (talk) 08:36, 15 August 2013 (UTC)

One star has to be at least about 25 times heavier than the other in order for some of the Trojan orbits to be stable. Other stable orbit possibilities are, as Someguy1221 pointed out, when the planet is much closer to one of the stars, or, as Icek pointed out, when the stars are much closer to each other than to the planet. Dauto (talk) 15:08, 15 August 2013 (UTC)

See circumbinary. Wnt (talk) 15:42, 15 August 2013 (UTC)

Thank you. 2.223.230.86 (talk) 00:31, 16 August 2013 (UTC)

nipples

Why do men have nipples — Preceding unsigned comment added by 67.197.49.21 (talk) 04:46, 15 August 2013 (UTC)

See Nipple#In_male_mammals. Someguy1221 (talk) 04:49, 15 August 2013 (UTC)

Men don't have nipples in South Carolina. It's against their religion. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:07, 15 August 2013 (UTC)

But opossums have a baker's dozen, so it evens out. Sadly, it is still far too few overall nipples, if you're a baby opossum. InedibleHulk (talk) 05:32, August 15, 2013 (UTC)

Basically, if there is no evolutionary advantage to not having them, it is more efficient to use the same DNA for males and females. For men to have nipples doesn't cause us any problems whatever in daily life - so there is no natural selection pressure that would eventually eliminate them. Evolution tends to put as little information as possible on the sex chromosomes for reasons of efficiency - so men and women tend to be identical in ways that don't matter to the perpetuation of our species. Even the organs that we do have that are visibly different are often relatively simple modifications of the same underlying design. Another example of that would be facial hair. Men typically grow full beards and mustaches - women still have hair in those places - it's just fine and short so it's (usually) barely noticeable. SteveBaker (talk) 12:04, 15 August 2013 (UTC)

It's a little more complex than that - there actually is a phenomenon of male lactation, and however insignificant it may be at this point in history, who knows how often natural selection calls on it on a geologic time scale? And, they're unarguably pretty, i.e. there's sexual selection, which maintains many a useless structure. Wnt (talk) 15:32, 15 August 2013 (UTC)

There is also male breast cancer, despite the "pinkness" the disease has in pop culture. Though rare (about 1% of breast cancer cases), it can strike even as "manly" a name as Rod Roddy. InedibleHulk (talk) 17:41, August 15, 2013 (UTC)

Butterfly Wings

I understand that a caterpillar turns into a butterfly after time- so here is my question: If I cut the wings of a butterfly, does it 'revert' back into a caterpillar? Why is it that when a butterflies wings are cut off, it flaps around and dies, instead of living it's old life as a caterpillar? Thank you. --Howdalikya eggsdone (talk) 15:05, 15 August 2013 (UTC)

It's programmed to behave like a butterfly, also it can't eat anymore. Count Iblis (talk) 15:11, 15 August 2013 (UTC)

Every part of the butterfly is made anew from imaginal discs - pupation is more than just popping out a pair of wings. The legs are different from those of the caterpillar and the prolegs it used to help hold on are just gone, and the mouthparts are also changed for new foods. Wnt (talk) 15:28, 15 August 2013 (UTC)

I'm not an expert, but the way I understand it, the caterpillar can be viewed roughly like a highly evolved "egg". The butterfly actually hatches out of it. Vespine (talk) 22:54, 15 August 2013 (UTC)

No, that's not really accurate. Maybe the transition from caterpillar to adult has a certain amount in common with the stage at which mammalian embryos develop a stratum granulosum (the start of the thickened stratified epidermis) based on the arguable homology of T3 and ecdysone. But understand that adult tissues in many species begin with simple diploid 2n nuclei and develop into more "industrialized" cells with 4n, 8n, etc. nuclei that are big, highly functional, but not meant to replicate. For us, this transition is usually quite gradual and continuous, like liver cells that have a gradual gradient within the liver acinus. Many of our fastest replicating epithelial tissues never get the chance to go polyploid. But in insects there's a huge distinction between the fast-replicating imaginal disc, which is dividing for future use, and the polyploid and nondividing (and indeed rigid) external tissues, which are fully differentiated and finished growing. Still, it is an exaggeration of our more steady cell turnover, I would say. Wnt (talk) 03:59, 16 August 2013 (UTC)

I have no idea what the following was about. Wnt (talk) 03:59, 16 August 2013 (UTC) :

Please read the two questions together before answering. CambridgeBayWeather (talk) 01:16, 16 August 2013 (UTC)
The following discussion has been closed. Please do not modify it.

Is the daytime aurora visible in Northern Norway?

Or isn't it dark enough at Noon in Winter and you would need to go farther North to Svalbard to see it? Count Iblis (talk) 15:07, 15 August 2013 (UTC)

If you are north of the Polar Circle, it is quite possible to see the aurora at 'noon' - since the sun is below the horizon. I myself saw it around lunchtime in Bodø one January about a decade back, when I was working there for a short while.

The further north you go the more days of no sun there is, logically that gives you a better chance of seeing it. WegianWarrior (talk) 17:13, 15 August 2013 (UTC)

Yes, but then given how extremely expensive Norway is, I'm not going to stay there for long (I paid 60 Euros for just a simple meal with potatoes vegetables and meat :( ). I was worrying about about the typical daylight aurora not being so bright as the evening one, combined with the fact that the Sun at Noon time not very far below the Horizon in Northern Norway, so you'll have some twilight that may drown out the aurora unless it is unusually bright. In Tromso the Sun will be only about 3 degrees below the Horizon around 21 December, while in Svalbard it will be 12 degrees below the Horizon.

But then I could go to Svalbard in Winter anyway to get to see a totally dark night sky for the first time in my life... Count Iblis (talk) 23:39, 15 August 2013 (UTC)

Electric rocket propulsion: propellants and ground based use

I read the Ion thruster & Electrically powered spacecraft propulsion articles, and I am not sure what prevents the use of air as a propellant. Why can’t one be used in a vehicle that runs on the ground? I know that chemical rockets & jets are not used in a medium sized ground vehicles like cars because of low efficiency and massive fuel consumption. But that shouldn't stop us from using an arcjet with air as a propellant, right? Diwakark86 (talk) 16:34, 15 August 2013 (UTC)

Those sorts of thrusters have a high propellant efficiency, but very low thrust. The majority of the examples listed in ion thruster have power outputs that don't compare favorably to a gasoline engine at all. Luckily, on the ground, we don't have to worry about propellant efficiency - instead of ejecting propellant to gain momentum we can just push off the ground with wheels. This is a very efficient way to transfer energy and it doesn't require propellant to be consumed. Also, the arcjet article mentions that the 100kW jet has a 10mile/sec exhaust - I don't think you want cars driving around with that coming out the back. The ion thruster article also explains that propellants are chosen for ionization properties and low erosion, you can't just replace xenon with air and have it work the same way. Jessica Ryan (talk) 16:53, 15 August 2013 (UTC)

For an example of an ion thruster that uses air as the propellant, see Ionocraft. --Carnildo (talk) 00:56, 16 August 2013 (UTC)

Chrysler Turbine Cars might be of interest here. While the exhaust wasn't nearly as fast as that from an ion thruster, it's heat was still problematic, as was the noise. That technology was used in the M1 Abrams main battle tank, though, where heat and noise are less problematic. StuRat (talk) 07:02, 16 August 2013 (UTC)

That Chrysler is a really interesting car - I never realized that any manufacturer developed a gas-turbine car all the way to being basically production-ready! Old helicopter turbines show up in boats every so often, and I think I read about Jay Leno driving a motorcycle that someone managed to fit one into... However, I read the question as using the rocket effect to accelerate - gaining forward momentum by putting an equal amount of momentum into the propellant, which is ejected. A gas turbine car still moves by pushing wheels against the ground. I suppose you could duct an ion thruster through a turbine and use that to get power to the ground, but I have a feeling it is a lot more efficient (and simpler/cheaper) to use the electricity to run an electric motor instead. Jessica Ryan (talk) 11:46, 16 August 2013 (UTC)

August 16

Identification of bug

I found this bug on the wall next to my front door this afternoon. Any idea what it is? NealCruco (talk) 00:29, 16 August 2013 (UTC)

That's a nice katydid, note the long antennae. Generally a harmless and interesting insect. Getting any more specific than that will might require some location information, and perhaps a sample specimen and Identification key. SemanticMantis (talk) 01:20, 16 August 2013 (UTC)

Maybe a common true katydid: Pterophylla camellifolia? Vespine (talk) 02:11, 16 August 2013 (UTC)

Well, I live in the CST time zone of the US. Is that specific enough? NealCruco (talk) 20:02, 16 August 2013 (UTC)

Vacuum pump

Do foot operated manual vacuum pumps exist, which are able to attain partial pressures involved in Büchner filtration? Plasmic Physics (talk) 01:54, 16 August 2013 (UTC)

Could you state the level of vacuum needed, in case someone is more familiar with pumps than with the particular process? Lots of gas chemistry was done in the 19th century with manually operated equipment. Hard vacuums were achieved with mercury operated pumps rather than mechanical pumps. Edison (talk) 14:23, 16 August 2013 (UTC)

The article on the process says an aspirator will work.I would call it a "suction" rather than a vacuum process, so comments about high vacuum do not apply. Foot operated aspirators are available, though the supplier I found is a wholesaler. See Medical foot operated manual vacuum aspirator where the FOB price is stated as $30-$180, so shop around. If you are handy, it might be possible to alter a typical foot operated inflator pump so that it acts as a suction pump. Here is a different design of foot operated aspirator which produces 300 mm of suction. There are also venturi suction devices which use the flow of tap water through a device to create suction, and cost about $7. Edison (talk) 14:44, 16 August 2013 (UTC)

Water-tap aspirators are pretty commonly used for this application. I've had problems with these sorts of filtrations when the vacuum source is pulsed rather than a more constant pull, but it depends on the nature of the liquid, solid, and filter-medium being used.. DMacks (talk) 15:28, 16 August 2013 (UTC)

The idea is to save on utilities, I don't want to be running up my parents' bills. I'm visualizing something like a spinning wheel - a pump which converts reciprocal motion to rotational motion.

Meaning, I'm not going to waste perfectly good water. Plasmic Physics (talk) 05:01, 17 August 2013 (UTC)

The spinning wheel is supposed to function as a fly wheel, preventing a pulsed vacuum. Plasmic Physics (talk) 08:12, 17 August 2013 (UTC)

'Suction'/vacuum', 'tomato'/'potato'. Thanks, I'll have a look at those. Plasmic Physics (talk) 01:09, 17 August 2013 (UTC)

Gingko biloba cutting

I took a 12 in. cutting from a tree a few weeks ago and have kept the proximal end in water ever since. For about 2 weeks it was doing fine and all the leaves remained moist and green and everything nice. But then, without warning, it shriveled and now I had to throw it out. Anything I should have done differently? My plan was for it to sprout rootlings and then I could plant it in soil and get a tree eventually by transferring it into a backyard. DRosenbach ^{(Talk | Contribs)} 03:48, 16 August 2013 (UTC)

Maybe should have used Indole-3-butyric acid? See cutting (plant). Wnt (talk) 04:03, 16 August 2013 (UTC)

Using water alone to propagate woody plants is always going to be problematic. The time taken for roots to appear is almost always longer than the time that mould or fungus takes to infect the cutting. This page suggests (1/3 way down) 15 centimetre cuttings of semi-ripe wood in summer in a cutting compost, this is a standard procedure for woody subject. My intuition tells me that gingko biloba are not that easy to root but I can't point you at a citation. Good luck, they are very interesting trees. Richard Avery (talk) 06:27, 16 August 2013 (UTC)

I'm about to stick a few cuttings in the ground. Spring soon where I am. I shall let you know in three months time. HiLo48 (talk) 07:07, 16 August 2013 (UTC)

As per above, I'd use some rooting hormone, and a little fungicide (neither of which has to be noxious). Rooting woody plants in water-only is often a bad idea, but they also must not be allowed to dry out in the first several weeks. Finally, a fun trick: Salix spp. root very well in pure water, and that water can then be used to root other plants, since it will have dissolved hormones from the willow! SemanticMantis (talk) 13:26, 16 August 2013 (UTC)

Ginko is a very primitive type of plant and is very different from other more advanced broadleaved trees. Our article Ginkgo biloba says; "most intentionally planted ginkgos are male cultivars grafted onto plants propagated from seed, because the male trees will not produce the malodorous seeds." The fact that cultivated root-stocks are grown from seed suggests that it's probably not easy to propagate it from a cutting. Alansplodge (talk) 13:36, 16 August 2013 (UTC)

But apparently it can be done: "The Ginkgo can also be propagated by cuttings (best way to be sure of the sex). Take young or half-ripe wood about 15 cm long during May-July. Put these in a frame and keep moist. They usually start growing best in their second year. You may also take cuttings of mature wood of the current year's growth. Shoots about 15-30 cm long are taken in December and placed in a frame. They should root in the spring."[6] Alansplodge (talk) 13:39, 16 August 2013 (UTC)

Fireflies completely gone from Indianapolis suburbs! Why?

Thirty years ago the suburban Indianapolis farm where my uncle has lived for nearly a century was teaming with fireflies at at least three or four per square foot on August nights. Today there are NONE. I stood outside wandering around the three acre plot for four hours and did not see a single firefly. I do not believe the explanations in http://www.firefly.org/why-are-fireflies-disappearing.html because there is no light pollution here: the same lights are in the same place and the road traffic is the same volume as it was 30 years ago. What do the reliable peer reviewed sources say about this tragedy? 98.220.133.91 (talk) 05:09, 16 August 2013 (UTC)

Indy got hit hard by the 2012–13 North American drought--Digrpat (talk) 09:42, 16 August 2013 (UTC)

True, but we also did here in central IL, and we had a fine firefly season this year. Actually, it peaked almost a month ago, and there are very few left. So perhaps the OP might have found a few round last month? SemanticMantis (talk) 13:27, 16 August 2013 (UTC)

Our article does say that they prefer "marshes or in wet, wooded areas"...so I could imagine a drought hitting them hard. SteveBaker (talk) 15:44, 16 August 2013 (UTC)

If it is a working farm I would ask about recent pesticide usage. Wnt (talk) 19:16, 17 August 2013 (UTC)

identify a plant

Can anyone identify this plant, please? I found it growing in the gap between two concrete slabs in my walkway, in St. Louis, Missouri.—msh210℠ 07:07, 16 August 2013 (UTC)

Pokeweed Phytolacca americana --Digrpat (talk) 09:23, 16 August 2013 (UTC)

Many thanks.—msh210℠ 18:23, 16 August 2013 (UTC)

Bom

How powerful would a bomb have to be for a tremor to be felt at the top of mount everest if it detonated at the deepest part of the ocean? 163.202.48.125 (talk) 12:09, 16 August 2013 (UTC)

Using this program, modeling the effects of an explosion as similar as one due to an impact (except for the air blast):

Input: Distance from Impact: 5000.00 km ( = 3110.00 miles ) Projectile diameter: 15.00 km ( = 9.32 miles ) Projectile Density: 8000 kg/m3 Impact Velocity: 30.00 km per second ( = 18.60 miles per second ) Impact Angle: 50 degrees Target Density: 1000 kg/m3 Target Type: Liquid water of depth 10.0 km ( = 6.2 miles ), over crystalline rock.

Energy:

Energy before atmospheric entry: 6.36 x 10^24 Joules = 1.52 x 10^9 MegaTons TNT

Seismic effects:

The major seismic shaking will arrive approximately 16.7 minutes after impact. Richter Scale Magnitude: 10.7 (This is greater than any earthquake in recorded history) Mercalli Scale Intensity at a distance of 5000 km:

IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.

V. Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.

Tsunami:

The impact-generated tsunami wave arrives approximately 4.5 hours after impact.

Tsunami wave amplitude is between: 255.0 meters ( = 837.0 feet) and 510.0 meters ( = 1670.0 feet).

Count Iblis (talk) 13:31, 16 August 2013 (UTC)

Bom 2

How powerful would a bomb have to be for a tremor to be felt at the deepest part of the ocean if it detonated at the top of mount everset? 163.202.48.125 (talk) 12:09, 16 August 2013 (UTC)

About as big as Bom 1 Caesar's Daddy (talk) 13:06, 16 August 2013 (UTC)

Much bigger, because you only get a big air blast; the seismic effects are then much less for the same explosion yield. Count Iblis (talk) 13:37, 16 August 2013 (UTC)

One problem is that Everest is a long way from the nearest ocean...and just about the opposite side of the planet from the Marianas trench (which is the deepest part of the ocean). That's a much bigger issue than whether you're at the top of a mountain or not. Another problem here is that you say "...for a tremor to be felt..." - you mean felt by a person? I guess their feet can't be touching the ground at the bottom of the deepest part of the ocean...so it's a bit hard to know how much seismic motion there needs to be under those circumstances. Is the person in a submarine? Either way, it's a heck of a lot more than if you were standing on the ground.

This document (which is talking about long distance seismic waves) says that "...larger power sources tend to produce lower frequencies." Unfortunately, humans are less good at detecting low frequency waves through our feet - a wave that moves the surface through (say) a millimeter over a time period of several minutes is detectable by instruments pretty easily - but not by humans. So we wouldn't "feel" the highest power sources. A very high frequency vibration of a tiny fraction of a millimeter is easy to feel...but that's not what you'll get here.

Underwater, you might feel a resulting tsunami - but not that far from land - and certainly not so deep.

The 1883 eruption of Krakatoa caused an explosion was estimated to be about 200 Megatons - four times larger than Tsar Bomba - the largest nuclear weapon ever made. Krakatoa is by far the largest explosion to have happened on earth in recorded history. It makes a great example of what could perhaps be achieved here.

That explosion was heard up to 3,000 miles away(!) - nowhere near far enough for your thought-experiment - so a guy sitting in a rowboat above the Marianas trench wouldn't hear it. Seismic instruments everywhere in the world measured the seismic waves - which looped around the world at least seven times before they faded too much to be measured. But those instruments are vastly more sensitive than people can feel themselves. Air pressure sensors also measured the change all around the world - but those effects wouldn't be noticable at the bottom of the ocean.

Smaller water waves were detected in fairly crude tidal gauges in the English channel - which is about as far from Krakatoa as you can get - so our guy in his rowboat might be able to detect it - but again, you wouldn't feel those at the bottom of the ocean - only in the surface layers of the water.

There don't seem to be any reports of people FEELING the explosion at ranges out at 3,000 miles where they could only just barely HEAR it...so people didn't feel the explosion on the other side of the world. It's pretty clear that 200 Megatons is nowhere near enough to do what you're looking for.

So the nearest I can get to a conclusion is that you need much MUCH more than 200 Megatons - which is already four times that of the biggest nuclear weapon ever manufactured.

The Valdivia Earthquake in Chile in 1960 (the largest earthquake in recorded history) produced seismic waves with 12 times more energy than Krakatoa - with an energy of around 2.7 gigatons - and even that was not felt by humans around the world - although it wasn't technically an explosion, so perhaps it doesn't count.

I doubt it can be done with any reasonable technology.

SteveBaker (talk) 15:31, 16 August 2013 (UTC)

One nitpicky detail: Everest is not really all that far from the Mariana Trench. Antipodes shows that the opposite side of the world from Everest is some distance off the west coast of Chile. The Trench is south of Japan and east of the Phillipines, and its antipode is somewhere around the coast of Brazil. As to setting off a bomb atop Everest, I would think Everest itself would absorb (and possibly be damage by) such a blast. Supposedly the crust under mountain ranges is much thicker than in the flatter areas of the continents, so the bomb would have to have the energy of a major earthquake - and that would take a huge amount of TNT. What humans can do pales by comparison with what Mother Nature can do. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:35, 17 August 2013 (UTC)

Neutron gamma gamma

The article Neutron gamma gamma was created on August 14, 2013 and says things like"When two gamma photons are in contact, and unlike charge state (+ -), [3], are engaged by the ultra-high electric hook." "The two photons gamma (gamma pair) move at the speed of light, but the ultra-electric hook bend their trajectories rotating them on a imaginary center mass " and "Stability of gamma pair becomes unbalanced at about 10.3 minutes (statistical), but not broken. [26]" Is it the gibberish it sounds like? Are there little "gamma gammas" spinning around which resemble the Yin Yang images?Individually there are a number of verifiable facts in the article, but is it overall an accurate depiction of a notable topic in physics, or is it original research? Edison (talk) 15:26, 16 August 2013 (UTC)

The article obviously needs either deleting or serious and ruthless editing, but I'm not sure which. We need a particle physicist. There is a process called Neutron-gamma (η,γ) otherwise known as Neutron capture, but we already have an article on this. Is User:MARCOS BUIRA PARDO trying to explain this, or some other process? Dbfirs 16:30, 16 August 2013 (UTC)

The phrase "neutron gamma gamma" - which I have never heard before - is never explained, or even used - and does not appear in any of the "references" listed at the bottom; so at the very least, we can say the article is improperly titled. The references themselves are mostly reasonable and reputable websites, but they do not validate the material in the article or mention the title. In other words, Template:Irrelevant_citation and Template:Failed_verification applies.

After trying to read two or three paragraphs, I am inclined to declare the page "patent nonsense," and at the risk of escalating accusations about my grouchiness, I recommend deleting the article. It satisfies several criteria for deletion, and I do not believe even generous editorial help can save the article. Nimur (talk) 17:23, 16 August 2013 (UTC)

It looks like nonsense, but not quite patent. I'd take it to AfD rather than {{db-nonsense}}. --Trovatore (talk) 21:12, 16 August 2013 (UTC)

So nominated per WP:DUCK. Clarityfiend (talk) 00:53, 17 August 2013 (UTC)

I expect little subatomic particles, however small would spin madly about their "imaginary center of mass," even if they were somehow oppositely charged but massless, and the article may contain numerous true and referenced statements and facts, but may not have a subject that satisfies WP:V and WP:N. The article creator's lack of fluency in English might be part of the problem. Edison (talk) 04:42, 17 August 2013 (UTC)

When a neutron star explodes (by nuclear reaction), what expelling? quarks or gamma photons. MARCOS BUIRA PARDO (talk) 14:07, 17 August 2013 (UTC)

Marcos, could you tell us what you read to get the information for this article? Are you describing Neutron capture? Dbfirs 07:33, 17 August 2013 (UTC)

Sorry for the confusion, I'm Spanish, I'm using Google translator. Neutron gamma gamma, is a neutron model not based on 3 quarks. But it has a precise mathematical support for size,energy and mass. Thank you very much.MARCOS BUIRA PARDO (talk) 14:07, 17 August 2013 (UTC)

Google translate is not really suitable for writing Wikipedia articles (though it is useful for translating articles into your own language). Perhaps you should write the article in Spanish and try is on the Spanish Wikipedia, but you will need to provide references. I wonder if the best place for alternative theories on neutron structure might be the article on Neutron. Dbfirs 16:22, 17 August 2013 (UTC)

How to compute the RGB values from the raw data of the camera?

As I understand it, a digital camera only has 3 sensors for each pixel with different spectral sensitivities. These don't correspond to the spectral sensitivities of the cells in our eyes, a linear transformation (the color matrix) is used to compute the RGB values and then some nonlinear transforms are used. However, I don't see how you could ever get the RGB values right if you only have 3 independent measurements that do not correspond to RGB.

So, the problem is that the "color space" of each pixel is infinite dimensional, because you have specify the amplitude of each frequency. Then what we perceive is always is the projection onto a 3 dimensional subspace, that subspace being defined by the spectral sensitivities of the cells that can detect red, green and blue light. But the camera has 3 different sensors, it project each pixel in a different 3 dimensional subspace. Count Iblis (talk) 18:07, 16 August 2013 (UTC)

SCIEN recently had an excellent presentation on this topic: essentially, a digital camera's electronics and computer is numerically inverting for several optical and physical processes, not least of which is the color filter array. Count Iblis correctly notes that the problem is underconstrained (in the pure mathematical sense of that word); this means that each implementer has to use a lot of heuristic tricks, leaving much room for error. I will see if the presentation video or slides are available to the public. Nimur (talk) 18:22, 16 August 2013 (UTC)

Thanks, it would be interesting to read more about this. I had not read into this issue before. It was only after I bought my Sony camera and the software for processing the raw files didn't work on my computer that I started to read about this. Alternative software is available but my camera isn't supported so I needed to find out about the way the colors are computed from the camera sensors. Count Iblis (talk) 19:22, 16 August 2013 (UTC)

Unfortunately the presentation I linked is available but non-free. In the interrim, we have a modest article on the generic color image pipeline; you can implement such a processing flow in software. The naive implementations for each stage are generally self-evident; the hard part is making algorithmic improvements that work without loss of generality. But if you're only processing a few images, this need not be an urgent concern. I'm not aware of any good free software implementations, but if you're willing to do a lot of manual work to tune up the results, dcraw can be used in GIMP; or if you prefer commercial software, you can download a Sony raw data plugin for Adobe Photoshop. Aperture (software) also works with Sony cameras, out of the box. Nimur (talk) 17:53, 17 August 2013 (UTC)

About running--------

If a person having weight 50 K.g.is running everyday in the morning about an hour with walking of 4 kilometers.He consumes less food than he want to eat.So what should be the effective change in the body? — Preceding unsigned comment added by Titunsam (talk • contribs) 18:17, 16 August 2013 (UTC)

There are many online sites showing how many calories you consume with exercise ([7] for example).

Basically, the calories from running for an hour will vary between about 470 to over 1000 depending on how fast you run. To get much over 600, you'll have to be running faster than most people can sustain for an hour - so 500 calories is probably a good number to go with. Walking 4km (2.5 miles) at a normal pace (around 2.5 mph) means that you're doing an hour of general walking - which consumes maybe another 180 calories. So you're consuming 680 from exercise. If you'd sat and watched TV for those two hours, you'd only have consumed around 220 calories - so you'd about 460 ahead of the game - which is about as much as one slice of pizza. (This is why exercise doesn't really excite me! I'd rather not bother with the exercise and eat one less slice of Pizza...but that's just me!)

It takes 3700 calories to make one pound of body fat - so you have to eat 3700 calories less than you burn in order to lose one pound.

So if you're only eating the barest minimum to keep your weight stable without exercise - then your exercise program should help you lose nearly a pound every week...which is a pretty good, sensible weight loss rate.

However, one extra slice of pizza per day - or a bag of potato chips every two days - completely wipes out the weight loss effect of all that exercise.

The problem is with "He consumes less food than he wants to eat". That's not a useful measure of what's good for you. If I eat whatever I want to - I'll go 500 calories over my ideal calorie intake every day. It only takes half a bag of chips to do that! And then I'll pack on a pound a week - and within a year I'll be seriously overweight.

To do this properly, you need to count and weigh EVERYTHING that passes your lips. Do this for a week - and by then you'll have a pretty good idea of what you're really consuming - in terms of calories.

For "numbers geeks" like me - I strongly recommend "The Hacker's Diet" - it's a great book that explains all of this clearly. Follow what it says to the letter and you'll lose a pound a week. Don't try to lose any faster than that though or you risk putting your metabolism into "starvation mode" - at which point losing weight becomes a major problem.

SteveBaker (talk) 19:04, 16 August 2013 (UTC)

That's what works for you, Steve. This is very individual. Some people eat less when they exercise, because exercise fills the void that they used to fill with the potato chips. (Or, in my case, there was I time I was controlling my weight by swimming, and I think part of the effect was that it made me just a tiny bit sick to my stomach and I didn't want as much lunch afterwards.) There was a period of a good number of years where I was able to control my weight with exercise alone, eating pretty much whatever I wanted. That's not true anymore, but it got me through at least five years consecutively, which is not to be dismissed lightly. --Trovatore (talk) 19:14, 16 August 2013 (UTC)

Yes, I agree. The hackers diet book does go into the science of this in some detail - and there is more to this than meets the eye. Personally, I find that exercise makes me incredibly hungry - so afterwards I'll want two more slices of pizza - and that doesn't just reverse the effects of exercise - it makes matters worse. Buy yeah - everyone is an individual. The best answers we can give are broad-brush. SteveBaker (talk) 19:30, 16 August 2013 (UTC)

Yes, and my own experience would point to the calory intake not being relevant for your weight (within a reasonable bandwidth) provided you exercise vigorougly almost every day. It doesn't make sense to me that an animal that has to survive in the wild would starve to death if due to changes in the environment it had to spend a bit more energy to get its food and if the amount it would find were a bit less. Obviously, it would just adjust its metabolic rate to keep its weight constant, warm blooded animals must have such a mechanism to avoid starving to death for such trivial reasons (note that 100 Kcal/day deficit = 46 kg weight loss in ten year time, but I'm sure I won't starve to death in ten years if I were to eat a sandwich a day less and increase the time I exercise a bit).

I measure everything I eat, I know that I eat close to 4000 Kcal per day now. I have increased my calory intake a lot it used to be just over 3000 Kcal/day a few years ago, and yet I have lost some weight, I used to weigh about 61 kg and I'm now at 58 kg. This is consistent with my idea that the body is designed to regulate itself, and eating until you are full is part of a normal healthy routine but then so is running for at least 30 minutes per day (I run for 50 minutes, 5 times per week). Why on earth would the signal for feeling hungry be wrong so that listening to it would undermine your health? To me that doesn't make sense at all. And if this is actually the case for some people, then these people have some health problem to begin with, which in most cases I believe is that they are couch potatoes. Count Iblis (talk) 19:44, 16 August 2013 (UTC)

Thermic effect of food

I read over here that digesting food requires calories. I was wondering if there's any food that requires more calories to digest than they contain. ScienceApe (talk) 21:08, 16 August 2013 (UTC)

See our Negative calorie food article. DMacks (talk) 21:13, 16 August 2013 (UTC)

August 17

Early gum disease

The Reference Desk does not give medical advice. Please ask your dentist for advice on your gum disease.
The following discussion has been closed. Please do not modify it.
Hello, I went to have a cleaning at my dentists and she said I "technically have gum disease (gingivitis)" on one or two of my teeth. They are the last teeth at the back of my mouth on the top and bottom, and they are a bit tender. She said to make sure I brush and floss twice a day, along with using a mouthwash, and I plan on doing so religiously. My dentist didn't say, and I have looked on the internet for an answer, but I can't seem to find a concrete one: how long does it usually take for the gums to stop being inflamed, and the general symptoms of gingivitis to go away? Thanks. 64.229.155.218 (talk) 04:21, 17 August 2013 (UTC)

using FASTA format

What's the meaning of the numbers in the 1st line of a particular sequence, like in the following example ?

>gi|5524211|gb|AAD44166.1| cytochrome b [Elephas maximus maximus] LCLYTHIGRNIYYGSYLYSETWNTGIMLLLITMATAFMGYVLPWGQMSFWGATVITNLFSAIPYIGTNLV EWIWGGFSVDKATLNRFFAFHFILPFTMVALAGVHLTFLHETGSNNPLGLTSDSDKIPFHPYYTIKDFLG LLILILLLLLLALLSPDMLGDPDNHMPADPLNTPLHIKPEWYFLFAYAILRSVPNKLGGVLALFLSIVIL GLMPFLHTSKHRSMMLRPLSQALFWTLTMDLLTLTWIGSQPVEYPYTIIGQMASILYFSIILAFLPIAGX IENY

Thanks, BentzyCo (talk) 16:05, 17 August 2013 (UTC)

These are accession numbers. The first one is an unique identifier for this sequence (GI number). The second one (after gb|) is an accession number. See [8] for details. 31.11.184.50 (talk)

Engine braking II

I recently (August 12, 2013) posted a question on engine braking and got satisfactory answers, thanks to all who responded. Well I soon realized it provoked a new question: why is it needed at all? The negative aspects are obvious: a lot of noise, no additional energy is returned to the battery (a parasitic effect as someone, perhaps SteveBaker, said), why not to use simple mechanical brakes we all have in our cars?

Thanks, - Alex174.52.14.15 (talk) 16:58, 17 August 2013 (UTC)

Because, as our article Engine braking says (confusingly in the Legal Implications section) it "can help save wear on friction brakes." Using conventional brakes alone will result in their wearing out more quickly (and as a driver I can attest that replacing brake pads is not cheap, whereas I've never had to replace an engine before changing the car for a newer one).

In a car the additional use of engine braking is never likely to be strictly necessary as opposed to merely aiding economy, but on a heavily loaded truck going down an incline, mechanical brakes in less-than-good condition alone might prove insufficient and/or fail entirely. {The poster formerly known as 87.81.230.195} 90.213.246.168 (talk) 17:28, 17 August 2013 (UTC)

The use of engine braking versus friction braking comes down to one thing:

Which is cheaper - clutch or brakes?

On a large truck, the answer turns out to be "clutch"...engine braking takes a toll on the clutch - but in a big truck, it's cheaper to replace than all of those wheels.

In your car, the clutch is much more expensive than a set of brake pads - so you should probably rely mostly on friction brakes.

That said - there is a problem with friction brakes - they dissipate the kinetic energy of the vehicle into heat in the brakes and brake pads. If they get too hot, the brake fluid will boil - then there are bubbles of steam in your brake lines and since steam is easy to compress (and brake oil isn't) - when you stomp on the brakes, nothing happens! This is called "brake fade" and it's dangerous and scarey as all hell! Hence you should ALWAYS use engine braking when coming down a long hill to avoid overheating your brakes. Race car drivers also use engine braking for the same reason - but they can use both and brake much harder than they otherwise could. (They likely replace the brakes and clutch after every race anyway).

SteveBaker (talk) 22:15, 17 August 2013 (UTC)

How can I use engine braking in my small Honda sedan?

- Alex — Preceding unsigned comment added by 174.52.14.15 (talk) 23:10, 17 August 2013 (UTC)

Downshift to a lower gear to slow the car down. RudolfRed (talk) 00:29, 18 August 2013 (UTC)

Dragonfly behaviour

I was up at a cottage (in Central Ontario) for the last week and, while there, I spent some time watching the dragonflies. At one point I saw some odd behaviour. Two fairly large dragonflies (I'm guessing common hawkers, but I'm no expert) were performing what I assumed was a mating flight, riding piggyback intermittently along the edge of a small lake (however, this indicates it's not nearly so straightforward as I thought). Afterwards, one of them began dipping itself into the water, but it was not dipping the tip of the abdomen, where any eggs would come out, but rather the thorax/legs area. It touched the water surface like so, then flew on a few inches and repeated, again and again for at least a few minutes. The abdomen was kept fairly stiff and definitely up out of the water. It was not hurt or having trouble flying (and there was a lot of vegetation it could have landed on if it was having trouble) and it performed at least a few dozen of these dip maneuvers before it flew off. It seemed to be aiming for open areas of water rather than tight against the water lilies. What was going on here? Dragonflies are (AFAIK) purely flight-based predators as adults, so it was not likely hunting anything. Given the fish population it was quite risky behaviour to engage in, so I'm assuming there's some reason behind it? Matt Deres (talk) 21:19, 17 August 2013 (UTC)

what substance is this

hello, we all know these electronic devices, mostly for computers, with a fancy casing that feels rubber-like or velvety to the touch. I have a DVB-T adapter like this. The thing is, its casing got sticky and somewhat gooey over time, I think because of this coating, whatever it is. What is it and is it dangerous (notorious plasticizers evaporating and whatnot?) Уга-уга12 (talk) 01:25, 18 August 2013 (UTC)